The contrasts of Mexico's southern and northern borders

FILE - In this July 14, 2013, file photo, pastors and others raise their arms on the San Diego side of a border fence during a cross-border Sunday religious service with others on the Tijuana, Mexico side of the fence. The Tijuana and San Diego border crossing is the world's busiest land border crossing, but also now sees relatively few illegal crossings. (AP Photo/ Gregory Bull, File)

MEXICO CITY (AP) — Some 3,000 Central American migrants prepared to cross into Mexico from Guatemala on Friday with hopes of eventually arriving to the United States. Busloads of Mexican federal police were gathering in Ciudad Hidalgo and a Mexican military helicopter flew along the river in anticipation.

Here is a look at the differences between the Guatemala-Mexico border and the U.S.-Mexico border between Tijuana and San Diego where members of a migrant caravan arrived last spring.

WHAT'S THE GUATEMALA-MEXICO BORDER LIKE?

The official border crossing is a bridge connecting the cities of Tecun Uman, Guatemala and Ciudad Hidalgo, Mexico. A gate onto the bridge on the Guatemalan side was closed Friday and blocked by police. But rafts also cross the swift-moving Suchiate River, moving cargo and people between the two countries day and night, typically without much government interference. Locals said they had been warned by Mexican authorities not to carry people. At times Mexico has stepped up its immigration patrols along the border, but it has had more success patrolling the roads leading away from the crossing where migrants catch rides or walk along the roadside.

WHAT'S THE U.S.-MEXICO BORDER LIKE?

The U.S.-Mexico border between Tijuana and San Diego is the world's busiest land border crossing. It is also the most heavily fortified segment between both countries and now sees comparatively few illegal crossings. In some places in the area, the U.S. has installed three layers of walls and fencing. There is also bright lighting, roads patrolled by the Border Patrol and surveillance technology.